National Oceanic and
Atmospheric Administration
United States Department of Commerce


 

FY 1983

Drag measurements for first-year sea ice over a shallow sea

Pease, C.H., S.A. Salo, and J.E. Overland

J. Geophys. Res., 88(C5), 2853–2862, doi: 10.1029/JC088iC05p02853 (1983)


For a free-drift case a method is developed for simultaneously determining air (Ca) and water (Cw) drag coefficients by solving the vertically integrated stress balance equation for sea ice. The method allows the algebraic determination of Ca andCw from measurements of relative wind and relative current at single reference levels, from estimates of the densities of all three fluids and ice thickness, and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements. The method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag. One shortcoming of the technique is that if the relative wind and current are colinear, then only the ratio of Ca and Cw can be determined. Another is that the accelerations caused by other forces need to be independently determined. An experiment was conducted on a single floe in the eastern Bering Sea over the continental shelf during March 1981. The site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10-20 m diameter floes. Both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site: Ca at 3 m was 4.55 × 10–3 by the profile method, compared to 3.63-4.39 × 10–3 for slab, depending on assumptions; Cw at 1.1 m by profile was 24.2 × 10–3, compared to 18.3-22.0 × 10–3 for slab. The two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice. The instantaneous stress balance on the floe included contributions from material acceleration, Coriolis force, the two surface stresses, and sea-surface tilt relative to mean current and tide.




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